by Jeb Burnside
Even in a world of microchips and instant communication, keeping tabs on a piston engines relative health is more black art than science. The harsh truth is that the engine instrumentation most airframe manufacturers provide is little different from what was installed in a 1948 Buick. If youre flying an older airplane, it is from a 1948 Buick.
But aftermarket engine monitors have been around for two decades now and even a simple one can improve your knowledge of engine operation and health. Since we last examined monitors six years ago, there has been a virtual explosion in market penetration. These days, its rare to see a high-performance single or light twin that doesnt have at least a multi-probe EGT gauge and many have full-blown digital instruments that monitor every conceivable engine parameter.
You can even buy a software package dedicated to analyzing the stored data (see sidebar). Features abound in these gadgets but what will the $1500 or so (street price) basic instrument for a four-cylinder single–plus installation-actually mean in terms of capability and peace of mind? What options make sense for the average owner? How long will it take to pay for itself? And which monitor is best for you?
Some Basics: How Hot?
Engines get hot. If one get too warm, heat can destroy it faster than you can ask, Wheres the nearest runway? While the FARs require at least an oil temperature gauge, the traditional CHT gauge installed as standard equipment in even the newest airplanes measures only what someone decided was the hottest cylinder. That instrumentation-even if accurate-tells you nothing about whats going on in the other cylinders.
Any engine monitor worthy of the name will be wired to thermocouple probes installed at each cylinder. Each probe, either threaded into a standardized hole in the cylinder or mounted as a washer beneath a spark plug, measures that jugs CHT. Similarly, an EGT probe is inserted into the exhaust pipe a few inches downstream of the cylinder and clamped into place.
With multi-probe data, a monitor can determine how well each jug is being cooled. Monitors can also determine how rich or how lean the fuel/air mixture is. Using the monitor, the magneto switch and some basic engine knowledge, a pilot can advise a mechanic which spark plug needs to be cleaned or changed. And, if automatic rough develops at night far from an airport, an engine monitor might pinpoint the problem or determine that there really isnt one.
Engine monitors available for piston-engines use a basic presentation combining a vertical bar graph with alphanumeric data on a 2-1/4-inch or 3-1/8-inch screen. With a four- or six-cylinder engine, the instrument graphically presents the data for each jug using four or six vertical bars. Many monitors also display an additional bar dedicated to another engine parameter, say oil temperature or turbine inlet temperature (TIT) for a turbocharged engine.
Even entry-level models monitor voltage to advise the pilot on the electrical systems health, for example. Some popular options include monitoring oil temperature, outside air temperature, fuel flow, induction or carburetor temperature, turbine inlet temperature for turbocharged engines, manifold pressure and engine RPM, to name a few. For the most part, these options can be added after the instruments initial installation.
In scan mode, the monitor cycles through each of the cylinders and then moves through the other available information while continuing to display the basic vertical bar graph. One (GEM 602) or two buttons (all other monitors) on the face of the instrument are used both for configuring and managing its presentation. For example, you can use the buttons to set high/low alarms for various parameters.
In addition to the button, fully optioned monitors may have a separate toggle switch. The Electronics International UBG-16 uses such a switch when its data storage option, the MUX-8A, is installed while the JPI EDM series uses one when its installation includes fuel-flow data.
Engine monitors present an at-a-glance picture of each cylinders health using bar graphs with or without numbers for each basic parameter. But the real value-and one of the major differences between monitor manufacturers-involves what the instrument does with the data. For example, by comparing CHT values, the monitor can alert a pilot to potential shock cooling of the cylinders.
And by normalizing each element of the instruments basic bar graph and comparing one cylinders values to the others, a monitor can alert a pilot to any changes that may require immediate action. Some models also allow pilot-configurable alarms to flash when a parameter is exceeded. Correctly setting alarms for EGT and CHT can alert a pilot well before that expensive collection of engine parts turns itself into so much scrap.
Perhaps the most popular-and most misused-feature is automatically finding the leanest cylinder to set up the desired fuel/air mixture. As the mixture is leaned, the bars representing each cylinders EGT value increase until a peak value is reached. By flashing the vertical bar for that cylinder, the pilot is shown when that jugs mixture has peaked. He can then decide how far rich or lean of peak each cylinder should be and adjust the mixture accordingly.
Another feature that has become standard in high-end engine monitors is data logging. The data can be stored in non-volatile memory for periodic download or sent to a portable computer (laptop or palmtop) for real-time analysis or storage. This option can be invaluable when troubleshooting, say, a stuck valve or to help determine what happened after, well, something happens.
For this review, we have confined our research to instruments displaying a graphical presentation–bar graphs-of CHT and EGT parameters in real-time. Weve concentrated on TSOd products for which STCs for many makes and models exist. Theres nothing preventing an owner from using the field approval process to install some of the newer, more interesting devices, other than time, money and frustration.
Since Aviation Consumer last looked at the market for these devices in 1998, much has changed. Several offerings have evaporated and two new manufacturers, Avidyne and Vision Microsystems, have joined the fray with TSOd, full-featured instrumentation with large-format displays. All prices given here are retail; you may be able to find a better deal at your local avionics shop or at a major trade show.
Avidyne is well known for its flat-panel multi-function and primary flight displays. However, the companys EX5000 MFD with optional EMax engine monitor being factory installed in Cirruses, Lancairs and six-seat New Piper singles, offers an engine monitoring capabilities new to this market.
The EMax option for the EX5000 puts all engine instrumentation plus system gauges onto one easy-to-read color display. Values for EGT and CHT are displayed in color-coded vertical bars–green for good, red for bad–and the EMax monitor for the EX5000C also includes a graphical fuel totalizer, a lean acquire mode and a percent horsepower display.
At start-up, the initial fuel page appears, allowing the pilot to enter the total fuel on board. An integrated fuel totalizer monitors fuel flow and computes fuel remaining, fuel to waypoint and fuel to destination. All six CHTs and EGTs, RPM, manifold pressure, oil temperature, oil pressure, fuel flow, outside air temperature, and electrical bus voltages are also monitored and displayed. The engine parameters are displayed using a traditional analog gauge presentation with its numeric value below. A dedicated engine monitor page shows all engine settings and parameters at a glance. The unit also displays engine and fuel data in data blocks on the full-screen moving map display. If a parameter is exceeded, its highlighted for immediate attention. The engine monitor also includes data storage of critical engine performance parameters of up to 30 hours of recorded data.
Unfortunately, the Avidyne EMax engine monitor is only available as an option with the companys full-boat EX5000 MFD. Equally unfortunate, the best way to buy one is in a new airplane. A retrofit program is available for early Cirrus SR20 owners who want to remove their existing Arnav MFD and replace it with the Avidyne. The price of that retrofit, including the EMax option, is $17,260, minus a $2500 trade-in allowance on the Arnav box. Cirrus SR20 owners will still need a harness and set of probes from Cirrus.
Physically, the unit can be installed in other aircraft already in the field, but the cost of engineering the software make it impractical. Avidyne tells us they are working on a unit designed for retrofit in the field, but could not say when it might be available.
Electronics International manufactures an array of aircraft instruments ranging from primary engine gauges to dedicated EGT or CHT instruments and to fuel flow management devices. The principal engine monitor product marketed by EI is the UBG-16, UBG meaning Ultimate Bar Graph and 16 the number of channels or probes the device can handle. EIs 2-1/4-inch unit was one of the first on the market to combine a graphical presentation with digital EGT and CHT values in real-time.
Rather than configure its connectors as dedicated to one specific kind of probe-a CHT or oil pressure probe, for example-the UBG-16 allows all 16 of its channels to be used as the operator chooses.
The UBG-16 ($1717, four-cylinder; $1953, six-cylinder, both prices include the separate MUX-8A memory module) handles all of the typical measurements of this instrument category such as CHT, EGT, oil temperature and so on but it can also be used to monitor RPM, manifold pressure, amperage and gyro vacuum/pressure.
Monitoring some of these parameters with other manufacturers devices means either upgrading to a higher-end and more expensive model or adding a separate instrument. None of the other manufacturers of which were aware offer STCd devices with the ability to display amperage or gyro-related values.Like the other monitors available, the UBG-16 displays a real-time graphical presentation of EGT and CHT for up to six cylinders, plus a seventh user-configurable column.
If 16 channels of data are not enough for you, EI offers several stand-alone instruments that can function as replacements for factory gauges. EI does not manufacture a single model for twin-engine aircraft; two UBG-16s are the way to go or spend $250, plus installation, to add the ability to switch from one engine to the other on a single display.
Data logging is not included in the basic UBG-16. Instead, EI offers a self-described black box data recorder, the MUX-8A, as an add-on device for those who want to store engine data generated by the UBG-16 for later download and analysis. The MUX-8A has four interval settings-one, three and six minutes, plus a burst mode for storing data every five seconds.
The unit can store between 690 to 115 hours of data in the first three modes and 10 to 15 hours in burst. Interestingly, the UBG-16/MUX-8A combination can be set to go into burst mode only when a pre-set parameter–say a red-lined CHT–is detected. If you buy the MUX-8A with the UBG-16, its only $50; bought separately, it retails for $395. In addition to the UBG-16s data, the MUX-8A can also be used to store data from other EI instruments after adding a $98-per-gauge RS-232 data option.
Like Electronics International, Insight has been around the avionics and engine monitoring market for some time. In fact, Insights original GEM 602 unit, circa 1982, was the first to provide simultaneous electronic display of all EGT and CHT engine information. In the engine-monitor category, Insight presently offers three basic flavors: The GEM (Graphic Engine Monitor) 602, the GEM 610 and the GEM 1200.
The GEM 602 is a basic six-bar graph instrument that doesnt display alphanumeric information; the GEM 610 adds to the six vertical bars with alphanumeric information for each cylinder and the GEM 1200 is a twin-engine version of the 610. All except the 1200 are 2-1/4-inch instruments; the 1200 requires a 3-1/8-inch hole. Any of these three instruments may be used on four- or six-cylinder engines.
While the GEM 602 ($1686, four-cylinder; $1826, six-cylinder) is a serviceable instrument, its omission of an alphanumeric presentation of engine data is a serious shortcoming, in our view, as is its inability to display any other data, such as outside air or oil temperatures. The 602 was a ground-breaking product in 1982. Two decades later, better instruments are available at the same price.
Those shortcomings are remedied, to an extent, by Insights other two offerings. The GEM 610 ($1785, four-cylinder; $1940, six-cylinder) has more features than the 602, including alphanumeric information for each cylinder, as well as trend indicators, outside and internal air temperature, dual TIT annunciators, something Insight calls a soft Hobbs meter/clock calendar, plus data logging and downloading via a wireless interface.
The GEM 1200 ($3312, four-cylinder; $3600, six-cylinder) uses its larger form factor to present the same data as the 610, simultaneously, for two engines. Both the GEM 610 and the GEM 1200 can be used as primary engine instrumentation for the parameters they monitor.
Unfortunately, Insight seems to have stopped improving its GEM series of engine monitors and has not kept up with other the companies innovations. For example, if you want to display anything beyond OAT and TIT in addition to the engines CHT or EGT, youre out of luck. GEM 602 users dont even have these few extra parameters, beyond EGT and CHT bar graphs. Many operators believe that tracking fuel flow and having it available in the stored data stream is valuable as a troubleshooting tool. If thats an objective, none of the GEM series can do it.
The only way to download data from the GEM 610 or GEM 1200 is to use the wireless infrared communications capability of a palmtop manufactured by Hewlett-Packard, the HP-95LX, -100LX or -200LX. The first of these products, the HP-95LX, was introduced in 1991; the -200LX was introduced in 1994. Any way you cut it, its been an eternity in the realm of portable electronic devices since these products came on the scene; HP stopped making them years ago. Still, these DOS-based machines are available-in used and refurbished condition-from links on Insights Web site. Nonetheless, technology seems to have passed by the GEM instruments.
J.P. Instruments (JPI) has perhaps the broadest range of full-featured engine monitors available for general aviation aircraft. At the low end ($1995, four-cylinder, $2195, six-cylinder) is JPIs EDM 700 (EDM is for engine data management) a 2-1/4-inch instrument for single-engine aircraft, followed by the EDM-760 ($3995, four-cylinder; $4495, six-cylinder) at 3-1/8 inches, for twins.
Also available is the EDM-800 ($3780, four-cylinder; $3990, six-cylinder), which adds fuel flow as a standard parameter and includes RPM and manifold pressure sensors, allowing a display of the horsepower percentage being asked of the engine. For aircraft with radial engines, JPI offers seven-, eight- or nine-cylinder models of the EDM-700. Yet another JPI offering for twin-engine airplanes is the EDM-750 and -850 packages, which use two -700 or -800 instruments, one for each engine. These range from $3995 to $8100.
All of these instruments are supplementary; they cannot be used as primary engine instrumentation. However, a fourth model, the EDM-711 ($2395, four-cylinder; $2595, six-cylinder), can be used to replace the original factory instruments after installing a separate annunciator panel with the yellow and red warning lights the FAA requires.
The -711s scanning mode also operates differently than JPIs other models. Existing EDM-700s can be upgraded by the factory to the -711 configuration. In fact, JPI offers a wide array of available upgrades and modifications for its in-service instruments, so many in fact that the chart (see sidebar) doesnt list them all.
Since our 1998 review, JPI made standard its then-optional data storage module. That component now allows recording between 25 to 1000 hours of data, depending on where the sampling rate is set between the low limit of two seconds and the high limit of 255. The JPI does not automatically shorten its data-collection interval when an alarm is triggered.
In our earlier review, we noted some grumbling about the user interface for the JPI. In particular, pilots dont seem to like the single-button interface and would prefer a multi-button design that allows some degree of backward and forward scrolling. Whether JPI listened to us or added a second button on its own, we dont know; all EDM instruments now have two buttons for configuring and controlling the display.
Like EIs UBG-16, all of JPIs models can be put into a scanning mode to cycle through the data received from connected probes other than those for EGT/CHT. This includes oil temperature, TIT, OAT, fuel flow, electrical bus values, among others.
Finally, by the time you read this, JPI may be able to offer TSOd and STCd products on a par with Avidynes EMax option. According to the company, its TSO/STC package is sitting on a desk at the FAA, awaiting approval for its EDM-900, -930, -930T and -950 models. Already available for the experimental market, these engine monitors are larger than most other products reviewed here, but with the exception of the EDM-950, which requires a separate MFD, they include color display screens and accommodate all parameters necessary for FAA certification as primary instruments. For panels with lots of real estate, these could be intriguing options.
Vision Microsystems TSOd VM1000 ($4360, four-cylinder; $4682.50, six-cylinder) uses a flat panel, high-contrast display to present engine parameters with both an analog gauge sweep and digital readouts. Data displayed includes RPM, manifold pressure, EGT/CHT, fuel flow, oil temperature and pressure, voltage and amperage. The tightly integrated 5.09 by 5-inch display panel is connected to a remote-mounted processing unit and the two boxes work together to not only present all the data necessary for aircraft operation but also provide alerts and per-flight data-logging of high/low parameters.
Although its TSOd, the VM1000 is wildly popular with the experimental segment. In fact, Vision Microsystems originally came had a non-TSOd version but after repeated requests, the company obtained TSO approval in 1998. As a result, Diamond Aircraft and Aviat Aircraft equip their new airplanes with the VM1000.
The same reason the VM1000 is popular among homebuilders -one solid-state instrument for monitoring all engine and aircraft system parameters-makes it relatively expensive and impractical to field-install in a certificated aircraft. Similarly, its physical size -more than twice as large as a standard single-engine monitor from other manufacturers–makes it problematic to find a place for it in most panels.
STCs exist for some aircraft, although Vision Microsystems does not own them. Still, if youve got the room and the budget, the VM1000 deserves a look.
If we were shopping for a new engine monitor for a piston single, we would take a close look at EIs offerings. We would be especially interested in the street prices available from various vendors for the basic instrument and the options we wanted. Our view is that EIs monitors are price competitive and quite capable.
Our main hesitation is its separate memory storage unit. But if data logging isnt important to you, the EI unit strikes us as the top value in a basic monitor.
But for overall best-of-best when data logging is desired, JPI stands out. Its products have become a de facto industry standard for good reason. The EDM series flexibility to monitor and store data on a range of engine parameters has far exceeded Insights products and inched slightly ahead of EI. The market reflects this. Additionally, we prefer JPIs all-in-one packaging of the monitor and its memory module to EIs separate black box and the additional installation and maintenance headaches the two devices may entail. JPIs memory storage and download functionality is about as seamless as it gets. Similarly, the ability to put so many engine and aircraft system parameters in one location helps reduce pilot workload.
At the back of the pack? Insights GEM series, in our view. JPI and EI have simply passed them by. We like the Avidyne and Vision Microsystems offerings but panel space and approvals make them impractical for certified airplanes at the moment. In a new Cirrus, the Avidyne EMax is a must-have and is a popular add-on option.
For a piston twin, the decision distills to panel space, or lack thereof. If theres room, we would opt for the EDM-760 over the GEM 1200 because of the additional parameters it tracks and the simpler memory download. If the smaller-size instruments were the only choice, wed go with two EDM-700s, to save on the cost of installing and maintaining two UBG-16s with their separate memory modules.
-Jeb Burnside is editor of Aviation Safety magazine, Aviation Consumers sister publication.